(1) Field of the Invention
The present invention relates to a method of producing a mask to be used for the production of a ceramic filter from a porous ceramic honeycomb structural body.
(2) Description of the Prior Art
In order to purify exhaust gases of internal engines of automobiles, there has been proposed a ceramic filter 1, which is produced by sealing selected through holes of a porous ceramic honeycomb structural body 2 having a large number of through holes 3 with a sealing material 4 at one end surface of the body and sealing remaining through holes, which are not sealed at one end surface of the body, with the sealing material 4 at the other end surface thereof as illustrated in FIGS. 1 and 2.
Methods of producing such ceramic filter are disclosed in U.S. Pat. No. 4,293,357 and EP No. 70,202A. That is, the prior art, as illustrated in FIG. 3, seals through holes at one end surface of a porous ceramic honeycomb structural body 2 having a large number of through holes and to seals remaining through holes at the other end surface thereof, by using a mask 5, having through holes 6 corresponding to given through holes to be sealed in the porous ceramic honeycomb structural body 2, arranged on the opening end surface of the ceramic honeycomb structural body 2, and injecting a sealing material 4 into the given through holes of the honeycomb structural body through the through holes 6 of the mask 5 by means of a pressuring piston 7 to seal the end portion of the given through holes of the body to produce a ceramic filter 1.
A known method for producing such a mask, utilizes a metal mold having convex portions at the position corresponding to the through holes of a honeycomb structural body, through which a sealing material is injected, and silicone or polyurethane is poured into the metal mold and cured therein (European Patent Laid-Open Specification No. 70,671).
However, a ceramic honeycomb structural body has already been strained or distorted during the forming or firing, and therefore even when the above described mask is elastic and freely deformable, it is difficult to adjust the mask to the opening end surface of all ceramic honeycomb structural bodies. Therefore a large number of metal molds must be produced. Particularly, in a ceramic honeycomb structural body having 5-60 through holes per 1 cm.sup.2. It is necessary to produce a metal mold which requires precise working, and the production of the metal mold is not inexpensive.